Between August 8 and 15, 2016, over 20 inches of rainfall fell over a large area of southeastern Louisiana and southern Mississippi. Latest estimates have between 40,000 and 110,000 homes damaged or destroyed across the state and 13 people dead. Climatologist and Professor of Geography Dagmar Budikova explores why these “1,000-year-storms” are becoming more frequent.

Budikova:

All weather events are brought about by two forcing factors today: natural variations and human influences. But, figuring out the respective proportion of each to any one event in particular is, however, a challenging task and an inexact science.

Starting in early March of 2016, slow moving storms brought significant moisture-rich air masses from the eastern tropical Pacific and the Gulf of Mexico to eastern Texas, Louisiana, and Arkansas. On August 14, the National Weather Service in New Orleans recorded over 15 inches of rain at Baton Rouge over a 72-hour period with rainfall rates peaking at 6 inches per hour. Thirty inches of rainfall were recorded in a small area west of Lake Pontchartrain, Louisiana. Flood stage levels remained high or extremely high in many areas for the majority of the past 6-month period, making the extraordinary flooding event more critical with each passing rain event. Tens of thousands of acres were flooded across a 200-mile area from Lake Charles to Franklinton in Louisiana.

Image from http://floodlist.com/america/usa/rain-bombs-thousand-year-floods-catch-americas-attention.

The Louisiana flooding adds to the other recent unprecedented 1,000-year flood events across the U.S. including Texas, West Virginia, Maryland, and South Carolina over the past six months. This prompts many to ask how this may be possible. These flood events have occurred during the same period that also recorded 10 consecutive months of new monthly global air temperature records, with July 2016 recorded as the warmest month since modern record keeping started in 1880.

We know that rising atmospheric temperatures prompt more water to evaporate from the ocean and remain in the atmosphere, increasing the amount of atmospheric moisture available for rainfall. Since the 1980s, we see extreme rain events becoming more intense and frequent across the country. In the southeast, heavy downpours have increased by almost 30 percent over the past 60 years.

Future climate predictions suggest that heavy rain events will continue to be more common and bring increased risk of flooding. Perhaps these rains and ensuing floods testify to a shift in our climate system and point to a different era of what we can expect and get in terms of weather, a new “normal.”